(1) Field of the Invention
The invention relates to a method of metallization in the fabrication of integrated circuits, and more particularly, to a method of polishing a metal stack in the manufacture of integrated circuits.
(2) Description of the Prior Art
Tungsten-plug metallization is well-known in the art. A conventional tungsten plug process of the prior art is illustrated in FIG. 1. Referring now to FIG. 1, there is shown semiconductor substrate 10. A contact, via, or trench is patterned into an oxide layer 20 to an underlying region 11. A metal film stack is deposited; for example, a titanium glue layer 22 is deposited over the oxide layer and within the opening. A titanium nitride barrier layer 24 is deposited over titanium glue layer. A layer of tungsten 26 is deposited which will form a plug within the opening. The metal film stack is then polished using chemical mechanical polishing (CMP) to remove the excess metal material, stopping on the oxide layer, as shown in FIG. 2.
Since titanium polishes much more slowly than tungsten or other metals, during the process of removing the titanium, severe erosion (illustrated by A), dishing (illustrated by B), and non-uniformity across the wafer occur. This makes the integration of metal CMP to manufacturing very difficult. All of these problems are extremely undesirable and adversely affect the electrical performance of the integrated circuit device. Unfortunately, there is no metal CMP process or CMP consumable set with a metal removal rate that has both low selectivity to titanium and very high selectivity to oxide.
It is desirable to use titanium not only as the glue layer but also for silicide and salicide processes. The titanium reacts with the underlying polysilicon in a contact application and forms titanium silicide which reduces contact resistance.
U.S. Pat. No. 5,502,008 to Hayakawa et al and U.S. Pat. No. 5,674,781 to Huang et al both show CMP of a titanium nitride/tungsten stack. U.S. Pat. No. 5,364,817 to Lur et al teaches forming a titanium nitride barrier layer under a tungsten layer where the barrier layer remains under an overlying aluminum layer. No CMP is performed. U.S. Pat. No. 5,595,937 to Mikagi discloses a CMP of a titanium nitride/titanium/copper stack with a stop on silicon oxide.